[WIP] Use path.join for toc source

[knownasilya]

WIP

Possible fix for docpress/docpress#169
Not sure about the replace line after, what would it be in windows? Would love to have some example paths for windows.

TODO

• Test on windows before merge.

[coveralls]

Coverage remained the same at 97.126% when pulling 1f9d6a0 on handle-toc-windows into 75f6c99 on master.

[Kikobeats]

@knownasilya what do you want to determinate if could be or not be merged?

[knownasilya]

This needs to be tested on windows before merge.

[cvax]

This is what I am getting on Windows 7 with this commit and the same repo for docpress/docpress#169.

 docpress serve

  Docpress
  starting development - ^C to exit

   err ✗    first build
    ✓ on    livereload
    ✓ on    http://localhost:3000

            Running

  ✗ docs\README.md: Unknown reference '../README.md'
    at fix (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\docpress-core\lib\fix_html.js:64:13)
    at Object.<anonymous> (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\docpress-core\lib\fix_html.js:41:29)

    at initialize.exports.each (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\cheerio\lib\api\traversing.js:300:24)
    at fixReferences (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\docpress-core\lib\fix_html.js:39:22)
    at fixHtml (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\docpress-core\lib\fix_html.js:15:3)
    at m (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\docpress-core\lib\index.js:241:7)
    at memoize (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\docpress-core\lib\memoize.js:19:15)
    at each (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\docpress-core\lib\index.js:239:15)
    at C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\lodash\_createBaseFor.js:17:11
    at baseForOwn (C:\Users\cvax\AppData\Roaming\nvm\v6.9.1\node_modules\docpress\node_modules\lodash\_baseForOwn.js:13:20)